1. Field of the Invention
The present invention relates to an apparatus for recording and/or reproducing information.
Particularly, the invention can be suitably used in an apparatus and method for recording and/or reproducing information to which a technique such as a scanning tunnel microscope or the like has been applied.
2. Description of the Related Background Art
In recent years, application of memory materials is a main stream in electronics industries such as computer and its related apparatus, video disc, digital audio disc, and the like. Development of the memory materials is also extremely actively being performed. Although the performances which are required for the memory materials differ depending on the applications, in general, the following points can be mentioned: (1) a density is high and a recording capacity is large; (2) response speeds for recording and reproducing are high; (3) an electric power consumption is small; (4) a productivity is high and a price is low; and the like.
Hitherto, a semiconductor memory using a semiconductor as a raw material and a magnetic memory using a magnetic material as a raw material are main memories. In recent years, however, in association with the advancement of the laser technique, a cheap recording medium of a high density by an optical memory using a thin organic film such as organic coloring matter, photo polymer, or the like has been proposed.
On the other hand, recently, a scanning tunnel microscope (hereinafter, abbreviated to an "STM") which can directly observe an electron structure of a surface plane atom of a conductor has been developed [G. Binnig et al., "Phys. Rev. Lett.," 49,57 (1982)], so that a real space image can be measured at a high resolution irrespective of a monocrystal and an amorphous. Moreover, the STM also has an advantage such that a sample can be observed with a low electric power without causing damage to the sample by a current. Further, the STM can also operate in the atmosphere and can be used for various kinds of materials. Therefore, applications of a wide range of the STM are expected.
The STM uses a principle such that when a bias voltage is applied between a probe (probe electrode) of a metal and a conductive substance and the probe is allowed to approach to a distance of about 1 nm, a tunnel current flows. The tunnel current is very sensitive to a change in distance between them. By scanning the probe so as to keep the tunnel current constant, various information regarding a whole electron cloud of a real space can be also read. At this time, a resolution in the in-plane direction is equal to about 0.1 nm.
Therefore, by applying the principle of the STM, the recording and reproduction at a high density can be sufficiently performed on the atom order (subnanometer). For instance, in the recording/reproducing apparatus disclosed in JP-A-61-80536, atomic particles adsorbed onto the medium surface are eliminated by an electron beam or the like and the writing operation is executed and the data is reproduced by the STM. Further, there have been proposed methods whereby the recording and reproduction are executed by the STM by using a thin film layer as a recording layer made of a material such as .pi. electron system organic compound or chalcogen compound class having a memory effect for a switching characteristic of a voltage current (JP-A-63-161552, JP-A-63-161553). According to the above methods, assuming that a recording bit size is equal to 10 nm, the recording and reproduction of a large capacity of 10.sup.12 bits/cm.sup.2 can be performed.